A color filter is an essential constituent part for a liquid crystal display or a solid-state imaging device.
Since the liquid crystal display is compact and has equivalent or superior performance as compared with the CRT as a display device, it is replacing the CRT as a television screen, a PC screen, and other display devices. Moreover, recently, as to the trend in the development of the liquid crystal display, it is changing from the conventional monitor application having a screen of a relatively small area to the TV application having a large screen and a higher image quality.
In the applications of a color filter for a liquid crystal display (LCD), its substrate size is enlarged for the production of the large scale TV, and for improvement in productivity where a large substrate is used, curability with low energy is required. Further, the liquid crystal displays for use in the TV are required to have image quality at higher levels than those for use in conventional monitors. That is, improvements in contrast and color purity are required. For improvement in contrast, it is desirable that the curable compositions used in the preparation of color filters use coloring agents (organic pigments and the like) of finer particles (see, for example, Japanese Patent Application Laid-Open (JP-A) No. 2006-30541). As a consequence, the amount of a dispersant to be added for dispersing pigments tends to increase. For improvement in color purity, it is desirable that the content of a coloring agent (organic pigment) in a curable composition with respect to a total solid content of the curable composition is higher. Accordingly, the content ratios of a photopolymerization initiator and a photopolymerizable monomer in the curable composition with respect to a total solid content of the curable composition tend to decrease.
Even in the applications for a color filter for a solid-state imaging device, curing with low energy is desired. In addition, a pattern film is thinning, which is accompanied with increase in the concentration of a pigment in the composition. In the pigment-based color filters, the pigments are becoming finer, and as a consequence, the proportion of a pigment dispersant in the composition tends to increase. To cope with problems such as color unevenness and the like caused by relatively coarse particles of the pigment, techniques wherein an organic solvent-soluble dye is used as a coloring agent in place of the pigment are proposed (see, for example, JP-A No. 2-127602). In such dye-based color filters, however, a polymerization inhibiting effect originating from the dye is becoming prominent as the concentration of the dye in the composition is increased.
Due to these factors, even in the case of any of a liquid crystal display and a solid-state imaging device, the contents of the photopolymerization initiator and photopolymerizable monomer that are components necessary for curing a curable composition are limited, then the concentration of the coloring agent therein is increased, and layer thinning is made difficult. In addition, desired sensitivity is hardly achieved due to a low proportion of polymerizable components, and desired developability is difficult to secure since there is no room for incorporation of a development regulating agent.
That is, thinning of a colored region, particularly, a colored pattern, is accompanied by an increase in the proportion of a pigment and a pigment dispersant in a curable composition, so that the content ratio of curable components (polymerizable materials) is made relatively low, rendering maintenance of high sensitivity difficult, and consequently the addition amounts of other components not involved in coloring or curing, such as a polymer of high acid value, and a development accelerator to be added for the purpose of securing developability, and the like, are necessarily reduced, resulting in a problem of inferior development.
Additionally, there have been attempts at securing sensitivity without reducing color property by reducing the amount of a pigment dispersant to be added while maintaining the content of a pigment, but here a new problem arises in that the stability of a pigment dispersion deteriorates to increase viscosity over time thus making formation of a uniform coating film difficult.
When the colored curable composition is thus used in formation of colored regions in color filters, particularly in color filters for solid-state imaging devices, it is necessary to satisfy both film thinning and color value, and therefore a colored curable composition having a higher pigment concentration and capable of achieving both sensitivity and developability is highly desirable.